Vital train movements include the required enforceable “movement authority” for a train operating on controlled track. This movement authority (data) must be transmitted from a controlling entity to the train, both at the trip origin and while the train is en route. Since this is critical train control data, the exchange of the data must be performed in a vital manner. Furthermore, the data onboard must be verified as being current at a frequent rate to avoid operating with stale or missing data.
Communications between the train and a controlling entity is expected to be over a wireless communications path where bandwidth considerations are paramount. Often, the available communications channels offer relatively low bandwidth and high-latency. Yet, this bandwidth is required to support data exchanges between the controlling entity and all the operating locomotives as well as all equipped wayside devices. Minimal communications latency is a key design consideration to deliver and maintain the vital data and react quickly to changes in the operating environment, such as loss of communications.